A solar cell for solar light generation start from various compounds such as silicon and the like, and can generate electricity in a solar cell type. However, even one cell does not obtain a sufficient output, and thus respective cells are connected in series or in parallel. This connection state is called a ‘solar cell module’.
The solar cell module is constituted by laminating glass, ethylene vinylacetate (EVA), solar cells, ethylene acetate (EVA), and a back sheet. The back sheet is laminated at the bottom in the module to block dust, impact, and moisture and thus serve to protect the solar cells. A Tedlar/PET/Tedlar (TPT) type back sheet is mostly used, and since a ribbon is used as a passage for allowing current to flow therethrough, a copper material coated with silver or tin lead is used.
The back sheet for a solar cell module is a key material which is attached on the outermost back surface of the solar cell module to protect cells. The back sheet needs characteristics such as durability, weather resistance, insulation, water vapor transmission, and the like, and manufactured by laminating a fluorine film and a PET film.
A fluorine film having superior weather resistance and durability is used. Currently, the Tedlar film formed of PVF resin, developed by the DuPont Company in 1961, has been used, but it is substituted with other films such as PET and the like by some manufactures due to high price and short supply.
EVA was developed as a material for a solar cell used in the satellite by NASA and the DuPont Company jointly in 1970. It is used as a standard of a sealing material for a solar cell. More than 70% of the world market is dominated by Japanese companies (Mitsui Chemical, Bridgestone, etc.). It serves to seal and fill cells inside the solar cell. It has superior strength, transparency, and insulating property.
For a polyethylene terephthalate (PET) film, a surface type plastic film having uniform thickness and constant physical properties is used, which constitutes a basic framework of the back sheet due to superior strength. It has superior physical, chemical, mechanical, and optical properties, and thus is widely used ranging from food packaging and office products to high-technology electrical electronic products such as semiconductor devices, displays, and the like. Recently, it has been increasingly used for a back sheet for a solar cell due to superior durability and weather resistance thereof.
Glass low in iron may be utilized to serve to prevent light reflection.
In the Tedlar/PET/Tedlar (TPT) type back sheet of the related art, a process of laminating the Tedlar film and the PET film through respective adhesives is needed, and a process of adhering the back sheet and the EVA film as a sealing material through a polyurethane adhesive or the like is further needed. Since the Tedlar film used in the existing back sheet is high-priced, it currently accounts for 80% or more of the manufacture process cost of the back sheet, which causes an increase in cost of the back sheet.
Therefore, studies on the polyester film that substitutes for the Tedlar film to lower the manufacturing unit cost have been actively conducted.
Korean Patent Laid-Open Publication No. 10-2011-0118953 (2011 Nov. 2) discloses that an ethylene vinyl acetate film adhesive layer is formed on a polyester film through in-line coating in order to substitute for the Tedlar film, and Korean Patent Laid-Open Publication No. 10-2011-0119134 (2011 Nov. 2) discloses that a hot-melt adhesive layer is formed on a polyester film through in-line coating in order to substitute for the Tedlar film. Korean Patent Laid-Open Publication No. 10-2011-0118271 (2011 Oct. 31) discloses that a fluorine-coating layer is formed by coating a fluorine-coating composition substituting for the existing Tedlar film on a polyester film through off-line coating, to thereby reduce the process and cost.
As such, conventional studies are about the formation of other functional layers for substituting for the Tedlar film.
In the solar light generation, characteristics needed for the back sheet may be adhesion, long-term durability, light reflectance for improving generation efficiency,
In the case of the sun light module, the generation efficiency is deteriorated with the rising temperature. Therefore, when a film having high light reflectance is applied thereto, the generation efficiency can be increased by blocking the temperature increase due to light reflection and recycling the solar light.
Therefore, a lot of studies on a back sheet for a solar cell module having high light reflectance and superior long-term durability are proceeding.